With the high cost of electrical energy required to operate air conditioners or heat pumps for cooling buildings, and particularly with the heavy demands for commercial building cooling systems at peak use hours, attention has been directed to various types of thermal energy storage systems. Such energy storage is advantageous since the building cooling and/or heating and process cooling may be generated and stored during off-peak hours at night when most businesses are normally closed, with the ambient outside temperatures being cooler and municipal power requirements reduced.
Most state of the art thermal energy storage systems are based on a solid to liquid phase change using energy storage in a narrow temperature range. Water based systems using ice storage are especially desirable because of low fluid costs and availability. However, the disadvantages of such systems include low evaporator temperature requirements because thermal gradient forces evaporator temperatures to a level far below 32.degree. F., also reducing the chiller efficiency, incomplete or low phase change, often in the order of about 50% to 55%, and low overall energy density of 80 BTU/lb. However, due to the exceptional environmental acceptability qualities and large availability, water is preferred above more corrosive, volatile, expensive and less readily available energy storage materials.